Hardware Reference
In-Depth Information
kernel_cutdown.img
This is the smallest possible Linux kernel that can be booted on the
Raspberry Pi. It contains minimal peripheral support outside of what is
absolutely needed to use the embedded devices on the Raspberry Pi.
It comes with a much smaller set of kernel modules than the standard
kernel image.
kernel_emergency.img
This is a Linux kernel image that contains a wide range of support com-
piled directly into the Linux kernel. Because so much support is com-
piled directly into this kernel, it can be treated as a “safe mode” kernel,
and it should boot properly even if the Raspberry Pi Linux userspace
has problems. The downside to this kernel image is that it is large in
comparison (9.2 M) and thus will have a performance impact. Also, it
does not come with any kernel modules, as all of the device drivers are
compiled into the kernel image!
Both of these alternative kernel images are built from the same source tree
as the normal kernel image and are present in the Git checkout ( firmware/
boot ). You can copy these to the boot partition using the same methods
described for the usual image. Simply change directory into the mounted
boot partition, rename any existing copies of these files to serve as backups,
and then copy the new files from the Git checkout into the mounted boot
partition.
Remember, if you want to boot into one of these kernels (or one of your
backup kernel images), just add an appropriate kernel= line to config.txt .
You might want to add multiple lines to correspond to different kernel im-
ages, but be sure to comment out any entries that you are not using by
prepending a \# character to the beginning of the line.
Now you can safely copy the new core Linux kernel image from your Git checkout onto
the boot partition (as root). You'll want to rename this file from kernel.img when you
do this (or rename the existing kernel.img in the SD card boot partition).
Install the Prebuilt Kernel Modules
Next, it is time to install the matching prebuilt kernel modules. You can find these
modules under the firmware/modules directory from your Git checkout. There will be
at least two directories here, and each will contain a version that corresponds to the
version of the Linux kernel used to build these images (and modules). At the time of
this writing, this version was 3.6.10, which shows as:
 
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